1. Field of the Invention
The present invention relates to a window glass antenna for automobile telephones and more particularly to a window glass antenna for transmitting and receiving vertically polarized radio waves for automobile telephones.
2. Description of the Prior Art
One conventional window glass antenna disclosed in Japanese laid-open utility model publication No. 5-82113 is illustrated in FIG. 7 of the accompanying drawings. As shown in FIG. 7, the window glass antenna, generally designated by the reference numeral 100, has a radiating pattern 101 extending vertically on a window glass panel, and a hollow grounding pattern 102 disposed on the window glass panel below the radiating pattern 101. The radiating pattern 101 has a lower end portion 101a connected to an end of the core of a feeding coaxial cable (not shown). The grounding pattern 102 has an upper central portion 102a connected to the braided shield of the feeding coaxial cable. The other end of the feeding coaxial cable is connected to an antenna terminal of an automobile telephone set or a radio receiver on an automobile.
FIG. 8 of the accompanying drawings shows the pattern of another known window glass antenna for automobile telephone as disclosed in Japanese laid-open patent publication No. 63-90306. The window glass antenna, generally designated by the reference numeral 110 in FIG. 8, comprises vertically spaced horizontal wires 111, 112, 113 disposed on a window glass panel, a joint wire 114 disposed on the window glass panel and interconnecting ends of the horizontal wires 111, 112, 113, a first feeding point 115 on the horizontal wire 113, an auxiliary antenna wire 117 extending vertically on the window glass panel between the horizontal wires 111, 112 and open opposite ends, and a second feeding point 116 on the lower open end of the auxiliary antenna wire 117 which is positioned closely to the first feeding point 115.
Since vertically polarized radio waves are mainly used for automobile telephone, the radiating pattern 101 (see FIG. 7), the joint wire 114 (see FIG. 8), and the auxiliary antenna wire 117 (see FIG. 8) are generally oriented vertically on the window glass panels. It is necessary to position these antenna elements as far from metallic automobile body components as possible to avoid an undesirable reduction in the reception sensitivity.
If these antenna elements are to be disposed above or below defrosting wires on the window glass panel, then it is necessary to provide a space which is vertically as long as the antenna elements above or below defrosting wires on the window glass panel, so that the antenna elements can be positioned in that space. Therefore, the defrosting wires may not have sufficient vertical dimension, and any defrosting area on the window glass panel may not be sufficiently large.
The window glass antenna 100 shown in FIG. 7 is required to have a certain pattern width because a frequency band handled thereby is determined by the widths of the patterns 101, 102. However, the required pattern width of the window glass antenna 100 may interfere with the vision of the driver of the automobile.